There has been a technique for estimating the position and the posture of a marker in an image by analyzing the image generated by capturing an image of the known marker with a camera, and determining the position and the posture of the marker relative to the camera.
Where the camera is located far from the marker, the marker is shown in a small size in an image. When the camera is moved or rotated, the marker might be located outside the field of view. Therefore, more than one marker is prepared, and measures are taken to show the markers in a relatively large size in the field of view of the camera.
For example, Patent Document 1 discloses a technique for enabling estimation of the position and the posture of a single marker relative to a camera by providing the single marker with a geometric feature. According to this technique, it is possible to switch between a result of estimation of the positions and the postures of markers relative to the camera based on the positions of the markers in an image, and a result of estimation of the position and the posture of a single marker relative to the camera, in accordance with the state of the marker(s) shown in the image.